Different types of wound dressing are required to meet different clinical needs. However, there are several desirable characteristics that are common to all wound dressings. Pain-free removal and the ability to remove a dressing without trauma to the wound and the surrounding skin are two of the most important characteristics. In order to prevent pain and trauma, the facing layer of a wound dressing needs to maintain a moist layer over the wound to prevent adherence to the drying wound. However, it is also desirable for a wound dressing to include some form of adhesive layer to maintain it in position. Island dressings are typically used, which comprise a so-called “non-adherent” or “low-adherent” absorbent pad with an adhesive retention layer over the top forming an adhesive border that sticks to skin surrounding the wound. However, repeated removal and replacement of such dressings can damage the peri-wound skin, ie the wound adjacent to the skin. The term “atraumatic dressing” is used in relation to products that, upon removal, do not cause trauma either to newly formed tissue or to the peri-wound skin.
There is an ongoing need to provide improved wound dressings. No single wound dressing product is suitable for use in all wound types or at all stages of healing.
Hydrophobic silicone gels of the type referred to as soft silicones adhere readily to dry skin but do not stick to the surface of a moist wound and do not cause damage on removal. As well as satisfying these principal requirements for use as the skin contact layer in atraumatic dressings, there are several other intrinsic properties of soft silicone that make it particularly advantageous for use in wound dressings. These properties are well-documented and include the fact that silicones are non-toxic, non-allergenic or -sensitising, feel soft on the skin and are conformable yet robust.
Numerous published papers describe the properties of silicone and the use of soft silicone dressings. Indeed, there are different types of soft silicone dressings currently on the market, including atraumatic wound contact layers, absorbent dressings for exuding wounds and also a dressing for the treatment of hypertrophic scars and keloids.
EP-A-0633757 is concerned with methods by which a dressing comprising a perforated carrier coated with silicone can be manufactured. That method involves blowing cold air onto the underside of the carrier to prevent silicone clogging the perforations. The carriers that are described are plastic films, and the document discusses the need to ensure good adherence between the silicone gel and the carrier. Measures such as the application of silicone primer, the use of microporous carrier films, and the use of a two-ply carrier comprising a plastic film laminated to a non-woven or textile material are suggested as ways of achieving this objective.
WO-A-2007/113597 describes laminates suitable for incorporation into wound dressings, which comprise a structural layer coated on one side with silicone gel and on the other with a pressure-sensitive adhesive such as an acrylic adhesive. Melt-blown polyurethane is used as the structural layer.
An absorbent dressing made from polyurethane foam is sold under the trade name Mepilex®. The outer surface of the foam is bonded to a vapour-permeable polyurethane membrane that acts as a barrier to liquids and micro-organisms. The inner surface of the foam is coated with a layer of soft silicone.
An absorbent, self-adhesive island dressing with a perforated soft silicone wound contact layer is sold under the trade name Mepilex Border®. The absorbent core consists of three components: a thin sheet of polyurethane foam, a piece of non-woven fabric, and a layer of super-absorbent polyacrylate fibres.
Another commercially available product, sold under the trade name Mepilex Transfer®, consists of a thin sheet of a hydrophilic open-cell polyurethane foam, coated on one surface with a layer of soft silicone and presented on a plastic film carrier.
The product sold under the trade name Mepitel® is a porous, semi-transparent wound contact layer consisting of a flexible polyamide net coated with soft silicone. This product is as described in EP-A-0261167, which describes an elastic, hydrophobic, knitted network coated with silicone gel. The structure of the knitted network provides openings that are not occluded by the silicone, and which thereby permit the passage of wound exudate in use.
The Mepitel® product has proven to be useful in many circumstances, but it does suffer from certain disadvantages. For example, production of the net to which the silicone is applied, which is done by warp knitting, is a relatively complex process, which is not amenable to the production of materials with widely differing sizes of opening. Also, because the knitted substrate is produced using a polyamide yarn, there is a danger of the product shedding fibre during use, which could contaminate the wound to which it is applied. A particular disadvantage of such products, however, is that they are of essentially fixed dimensions, with very little extensibility in any direction. This means that they do not conform well to the surface of an irregularly-shaped part of the body, eg a knee, with the result that when applied to such an area they may not remain in position and may be easily dislodged. A further disadvantage is that retention of the silicone gel on the substrate depends on the silicone fully encapsulating the substrate; failure of the silicone to fully encapsulate the substrate at any point might create a point of weakness at which the silicone may separate from the substrate, thereby impairing the performance of the product and/or leading to undesirable loss of silicone into the wound.
The present invention is directed to overcoming these and other deficiencies in the art.